This invention relates broadly to apparatus for sputter coating a substrate in the form of a disc.
Cathode sputtering is now widely used for depositing thin films of material onto substrates of many different configurations. The process generally involves ion bombarding a target of the material to be sputtered in an ionised gas atmosphere in an evacuable coating chamber. Vacuum is maintained in the chamber to cause particles of the target material to be dislodged and deposited as a thin film on the substrate being coated.
The coating of discs, for example magnetic discs used for data storage, is one particular field where sputter coating may advantageously be used, and there have been proposals for apparatus specifically designed to be dedicated to disc coating. One such proposal is summarised in the Journal "Research And Development" for March 1985 in an article by Richard E. Levine at pages 111 to 116 of that Journal. In the apparatus there described, discs are individually loaded in a clean room onto a disc support which holds the disc around part of the circumference thereof. Means are provided for moving the support from the clean room through a sequence of process chambers wherein the disc is cleaned and required materials are sputtered onto the discs. In each coating chamber the disc is positioned between two opposed targets so that both sides of the disc may be coated simultaneously.
The principal difficulties that are experienced with this apparatus stem from the method by which the disc is supported. The circumferential support system disclosed makes it extremely difficult to achieve the necessary firm grip on the disc without obscuring a part of the disc that requires to be coated.